Flow control is performed on ingress data packets when the incoming rate of the data packets over a given period of time exceeds the rate at which the data packets can be processed. The excessive incoming rate of data packets results in increased fill-levels of ingress queues to the data processing resources, any of which levels can cause flow control measures to be initiated when the level exceeds a predetermined threshold. One flow control technique used in data communications that is in accordance with the aforementioned principle is backpressure signaling.
A simple backpressure signaling technique is to use on-off signaling. According to this technique, a receiver queue of a data communications system, upon crossing a fill-level threshold, causes a backpressure signal (e.g. halt) to be generated that is sent to the source of the packets. The backpressure signal (halt) indicates to the source that it should suspend sending packets to that queue until further notice, which will be given in the form of another backpressure signal (e.g. resume). In some cases there can be more than one packet source, and in those cases the backpressure signal would normally be sent to all of those sources. A problem with this simple on-off backpressure signaling is that all traffic is treated identically. That is, high-priority, network-control traffic undergoes the same backpressure as low-priority, best-effort traffic, to the point where a flood of low-priority traffic can halt the flow of low-bandwidth, high-priority traffic. Impeding the flow of high-priority traffic can have service affecting implications such as network instability and lost data.
More advanced backpressure signaling techniques are known that use more than simple on-off signaling. These techniques include those that apply flow control to data packets of only certain priorities. According to such techniques, when the fill-level threshold of a priority-specific receiver queue is crossed, traffic of the corresponding priority is halted using on-off backpressure signaling. This approach is able to ensure that low-priority traffic does not impede the flow of higher-priority traffic. However, a disadvantage of this approach is that ingress bandwidth may go unutilized. For example, low priority traffic may be halted when a corresponding fill-level threshold is crossed even when no higher priority traffic is present.
Accordingly, there is a need to provide ingress traffic flow control that gives precedence to high-priority traffic over low-priority traffic while minimizing unutilized ingress bandwidth.